1. Field of the Invention
The present invention relates to an antenna apparatus for a portable terminal, and more particularly to an antenna apparatus for a portable terminal which has a variable movement antenna apparatus variably moving a position of a ground surface of the antenna.
2. Description of the Related Art
Generally, portable communication devices mean devices by which radio communication can be performed, while the devices are being carried. The portable communication devices include a hand-held phone (HHP), cordless telephone (CT-)2 cellular phone, a digital phone, a personal communications systems (PCS) phone, and a personal digital assistant (PDA) and are sorted into various types according to their shapes. For example, the radio terminals are sorted into a bar type, a flip type, a folder type, and a sliding type according to their shapes. The above-mentioned portable terminals always include an antenna apparatus, a data input and output device, and a data transceiver.
The data output device generally uses a liquid crystal display (LCD).
Basically, a plurality of keys are arranged on a key pad used for data input. The keys include a send (SND) key which is a communication start button, a cancel key, a clear key (CLR), number keys, letter keys, an end (END) key, function keys, a power (PWR) key, etc.
Recently, the number of subscribers of the portable terminals has explosively increased, and the portable terminals have become so demanded that almost all people carry portable terminals. Although at the beginning the portable terminals simply provided voice services, portable terminals providing a radio listening function, an MP3 function, a moving image display function, a remote control function, etc., are available now.
Portable terminals providing a camera, a high speed data communication, and a voice communication function have recently been developed. As these new devices demanded by consumers are mounted within the portable terminals, the space for built-in antennas becomes smaller as the mounting areas for the other devices become larger.
To accommodate the expanding volume required by these other devices, the antenna apparatus for receiving signals transmitted from callers and transmitting signals must be properly positioned in the portable terminals.
The antenna apparatus mainly includes a whip antenna and a helical antenna.
The helical antenna is generally used to lower the mounting height of the antenna. Different from a rod antenna in which a rod is drawn to extend the length of the antenna, the helical antenna has a protruding portion on one side and at the upper portion of the body of the terminal and is detachably fixed to the terminal. However, the terminal having the helical antenna does not have an attractive appearance due to the protruding portion of the antenna.
Recently, built-in antennas have become widely used in the terminals to overcome the above-mentioned disadvantages. A chip antenna, a planar inverted F antenna (PIFA), and a loop antenna are mainly used as built-in antennas.
As shown in FIGS. 1 to 4, the sliding type radio terminal 1 includes a body housing 2 having a main printed circuit board 2a, a sliding housing 3 slidably moved from the body housing 2, and a planar inverted F antenna 4 mounted to the body housing 2. The planar inverted F antenna 4 includes a radiation body 4a including an electric body formed on a main printed circuit board 2a in which a ground surface (not shown) is provided for an impedance value and shorting pins 4b. 
As shown in FIGS. 2 and 4, in the planar inverted F antenna, the radiation body 4a is installed so as to be separated from the ground surface by a predetermined height.
As shown in FIG. 2, the reason why the radiation body 4a is installed so as to be separated by a distance L1 (shown in FIG. 2) is because the distance L1 is an element influencing the radiation characteristics and gains of the antenna.
However, for the conventional sliding type portable terminal with the planar inverted F antenna installed, since the space required for mounting a plurality of parts for slidably moving the sliding housing from the body housing becomes greater, less space is available to provide separation between the ground surface and the radiation body due to the limited space in the terminal. Thus the efficiency of the antenna becomes lower and the miniaturization of the terminal is restricted.
Further, with the arrangement of the conventional sliding type portable terminal, if the sliding housing is slidably moved on the body housing, the front surface of the built-in antenna mounted into the body housing is screened, lowering the radiation efficiency of the antenna.